1. Field of the Invention
The present invention relates to automatic guided vehicles (AGVs), methods and apparatus for controlling AGVs, and use of an AGV as a computer peripheral device in a home or office environment already equipped with a computer.
2. Description of the Prior Art
Numerous devices and systems have been proposed for controlling an automatic guided vehicle (AGV) through a working environment. AGV systems have been successfully applied to specialized tasks such as warehouse automation, hospital delivery systems, and other industrial applications. There is a great deal of interest in using AGVs for automatic cleaning tasks. Despite extensive work and progress in the fields of AGV design, navigation, and control, the promise of ubiquitous cleaning robots suitable for ordinary household use remains substantially unfulfilled.
Most AGV systems described in the prior art use an onboard computer for control and guidance. U.S. Pat. No. 5,109,566 to Kobayashi, et al, describes a method for subdividing an area to be cleaned into a regular grid. As the AGV traverses the area, ultrasonic sensors detect the presence or absence of an obstacle within each grid square. The onboard computer system stores this information and uses it to guide the vehicle through the environment. A principal limitation of this system (and many similar systems, such as another taught by U.S. Pat. No. 5,305,217 to Nakamura et al.) is the high cost and/or limited capabilities of the onboard computer. If the vehicle includes an inexpensive computer, its storage, processing, and user-interface capabilities are necessarily limited. If the vehicle includes a computer system with plentiful storage and CPU resources, the cost of the system is increased beyond the reach of many consumers.
U.S. Pat. No. 5,111,401 to Everett, et al; teaches a method for AGV navigation using retroreflective strips applied to a floor to mark guidepaths. These strips are detected by a camera and image-processing equipment mounted on the vehicle. The cost of the camera and image-processing equipment render this system unsuitable for consumer applications. Furthermore, most household and office environments cannot accommodate strips applied to the floor.
U.S. Pat. No. 5,341,540 to Soupert, et al; teaches a cleaning system which requires an operator to manually guide an AGV through a desired path during a learning phase. A computer system on the vehicle memorizes the path so that the vehicle can later clean automatically. Any such system which requires a laborious, time-consuming, or error-prone installation process will be subject to substantial resistance from consumers.
The fields of AGV navigation and control have been extensively addressed in the prior art. A principal problem in AGV navigation is determining the position of the vehicle within the working environment. Dead-reckoning (a.k.a. odometry), a process in which wheel rotation counts and steering angle measurements are used to continuously update an estimate of the vehicle's location, is a standard technique. AGV navigation methods which rely exclusively on dead-reckoning tend to be severely limited by accumulated errors in the position estimate.
Some systems in the prior art use a secondary source of navigational information to correct accumulated errors in a dead-reckoning position estimate. U.S. Pat. No. 4,754,402 to Wand et al; teaches a method for using a vision system to provide an absolute reference for dead-reckoning navigation. Vehicles which include a vision system and associated computation and storage facilities are too complex and expensive for cost-sensitive applications.
U.S. Pat. No. 4,811,228 to Hyyppa teaches a navigation method which uses a plurality of anonymous, fixed retroreflective reference markers detected by a scanning system on a vehicle. During a learning phase, an operator guides the vehicle along a desired path and an onboard computer monitors the apparent motion of the reference markers and memorizes their locations. During a subsequent automatic operation phase, the computer can derive an estimate from observations of the reference markers. This system is limited because the vehicle must be within line-of-sight of at least three reference reflectors at every point along its intended path. This system is further limited because it requires that the operator precisely specify the path for the vehicle to follow.
The cited example systems suffer from high cost, an inconvenient installation process, or both. These factors limit their utility in home or small-business applications. That such systems have not been widely accepted for home or office use (as of the date of this application) despite much progress in the field of AGVs is significantly due to the high cost of the onboard computers used for guidance and control.
Traditionally, AGVs have been thought of as expensive systems suitable only for use in large factories or dangerous environments where the cost of the system is not a critical factor. Most improvements have been in the area of making AGVs more autonomous, or in developing sensing methods to determine their position more accurately-often through the application of expensive technologies or components.